Gas turbine engines (such as those used in electrical power generation or used in modern aircraft) typically include a compressor, a combustion section, and a turbine. Pressurized air from multiple stages in the compressor may be supplied to an environmental control system (“ECS”). A typical ECS may comprise flow and/or pressure regulating valves that reduce airflow and/or pressure of air bled off the high stage and low stage of the gas turbine engine. This air is conditioned (e.g., cooled and filtered) and then conducted to the cabin. As engine power output varies, the air pressure at a single location in the compressor may vary as well. Pressurized air for the ECS may be supplied from two or more different locations in the compressor. During low power output of the engine, the compressor pressure may be relatively low, and a relatively higher pressure location may be used to supply the buffer system. During high power output of the engine, the compressor pressure may be relatively high, and a relatively lower pressure location may be used to supply the ECS.